Summary
The question revolves around the behavior of lazy-loading images in HTML, specifically when an image is set to display:none by CSS and has a loading="lazy" attribute. The goal is to understand whether such an image will be loaded with the page, and if the positioning on the page affects this behavior.
Root Cause
The root cause of the confusion lies in the interaction between CSS visibility properties (like display:none) and the lazy loading mechanism. Key points to consider include:
- How browsers handle lazy loading for images that are not initially visible
- The impact of CSS positioning (e.g., fixed positioning) on lazy loading
Why This Happens in Real Systems
In real-world systems, this scenario occurs due to several reasons:
- Optimization techniques: Developers may use lazy loading to improve page load times
- Dynamic content: Websites may dynamically add or remove content, affecting what is initially visible
- Responsive design: Different screen sizes and orientations can change what is visible on the page
Real-World Impact
The real-world impact includes:
- Page load performance: Unnecessary loading of images can slow down page loads
- User experience: Delayed loading of critical images can affect user interaction
- Resource utilization: Loading unnecessary images can waste bandwidth and system resources
Example or Code
To illustrate the concept, consider a simple HTML structure:
This example shows an image that is lazy-loaded but initially hidden (display:none).
How Senior Engineers Fix It
Senior engineers approach this by:
- Carefully evaluating the visibility and positioning of elements
- Using browser developer tools to inspect the loading behavior of images
- Implementing IntersectionObserver API or similar techniques to manually control lazy loading for dynamically added or hidden content
Why Juniors Miss It
Junior engineers might miss this due to:
- Lack of experience with lazy loading and its interactions with CSS properties
- Insufficient understanding of how browsers optimize resource loading
- Overlooking the impact of CSS positioning on the visibility and loading of elements